Carbon dioxide detector having borosilicate substrate

ABSTRACT

The present disclosure relates to a carbon dioxide detector having a borosilicate substrate. It may also have a carbon dioxide responsive indicator solution disposed on the borosilicate substrate. The carbon dioxide detector may be part of a carbon dioxide detector system also including an air intake operably connected to the housing to allow air to reach the carbon dioxide detector. The carbon dioxide detector may include a borosilicate substrate and a carbon dioxide responsive indicator solution disposed on the borosilicate substrate. This detector may be part of a further system, such as a resuscitation system. The detector may be made by wetting a borosilicate substrate with a carbon dioxide responsive indicator solution and drying the indicator solution to immobilize it and form a dried carbon dioxide detector. It may be used to detect the concentration of carbon dioxide in an air sample by exposing the detector to the sample.

TECHNICAL FIELD

The present disclosure relates to a carbon dioxide detector having aborosilicate substrate.

BACKGROUND

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present invention,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

Respiratory gasses may be readily distinguished from non-respiratorygasses by carbon dioxide content. Exhaled respiratory gas in a humantypically contains between 3% and 5% carbon dioxide. In contrast,ambient air has only approximately 0.03% carbon dioxide. Normalesophageal gas has similarly low levels of carbon dioxide.

The detection of respiratory gasses via carbon dioxide content may beuseful in a variety of circumstances. For example, one may determinewhether an endotracheal tube has been correctly placed in the trachearather than in the esophagus by detecting the presence of carbon dioxidein air exiting the tube. If carbon dioxide levels consistent withrespiration are present, then the tube is correctly placed. If only lowcarbon dioxide levels consistent with placement in the esophagus arepresent, then the tube may have been incorrectly placed and may need tobe removed and reinserted correctly. Additionally, if a tracheal tube ispresent in the trachea, but carbon dioxide levels in respired gas arelow, this may be indicative of perfusion failure.

Continued detection of carbon dioxide in respired gas may also be usefulin determining if an endotracheal tube has been dislodged and ifbreathing and perfusion continue to be normal.

Current products can detect carbon dioxide in respired air using variouschemicals sensitive to the presence of carbon dioxide on a substratesuch as cellulose filter paper, for example Whatman paper.

SUMMARY

Certain aspects commensurate in scope with the disclosed embodiments areset forth below. It should be understood that these aspects arepresented merely to provide the reader with a brief summary of certainforms the invention might take and that these aspects are not intendedto limit the scope of the invention. Indeed, the invention may encompassa variety of aspects that may not be set forth below.

The present disclosure relates to a carbon dioxide detector having aborosilicate substrate.

In one embodiment it relates to a carbon dioxide detector having aborosilicate substrate and a carbon dioxide responsive indicatorsolution disposed on the borosilicate substrate.

In another embodiment it relates to a carbon dioxide detector systemhaving a carbon dioxide detector, a housing containing the carbondioxide detector, and an air intake operably connected to the housing toallow air to reach the carbon dioxide detector. The carbon dioxidedetector may include a borosilicate substrate and a carbon dioxideresponsive indicator solution disposed on the borosilicate substrate.

In another embodiment it relates to a carbon dioxide detector systemhaving a means for detecting carbon dioxide. The means may include aborosilicate substrate. It may also include a housing means to containthe means for detecting carbon dioxide and an air intake means operablyto allow air to reach the means for detecting carbon dioxide.

In another embodiment it relates to a resuscitation system having acarbon dioxide detector system, a resuscitator housing fitted with thecarbon dioxide detector system, and a bag attached to the resuscitatorhousing. The carbon dioxide detector system may have a carbon dioxidedetector, a housing containing the carbon dioxide detector, and an airintake operably connected to the housing to allow air to reach thecarbon dioxide detector. The carbon dioxide detector may include aborosilicate substrate and a carbon dioxide responsive indicatorsolution disposed on the borosilicate substrate.

Another embodiment relates to a method of manufacturing a carbon dioxidedetector. The method may include wetting a borosilicate substrate with acarbon dioxide responsive indicator solution and drying the indicatorsolution to immobilize it on the substrate and form a dried carbondioxide detector.

Another embodiment relates to a method of detecting carbon dioxideconcentration in an air sample. The method may include exposing a carbondioxide detector to the air sample. The carbon dioxide detector mayinclude a borosilicate substrate and a carbon dioxide responsiveindicator solution disposed on the borosilicate substrate. The methodmay also include determining the color of the indicator solution,wherein the color of the indicator solution indicates the carbon dioxideconcentration in the air sample.

Still another embodiment relates to a carbon dioxide detector having acarbon dioxide responsive indicator solution disposed on a borosilicatesubstrate. The detector may retain acceptable carbon dioxide sensitivityfor at least 7 days at a temperature of approximately 60° C.

Another example method relates to detecting carbon dioxide in abreath-to-breath manner. To perform this method, one may attach to asubject a carbon dioxide detector having a carbon dioxide responsiveindicator solution disposed on a borosilicate substrate. One may measurethe carbon dioxide in respired air at an interval corresponding to everybreath of the subject.

Yet another example method of detecting carbon dioxide includesproviding an air sample to a carbon dioxide detector having a carbondioxide responsive indicator solution disposed on a borosilicatesubstrate. One may measure the carbon dioxide in the air sample in atime frame between approximately 1 to 20 seconds.

Another embodiment relates to a carbon dioxide detector having a carbondioxide responsive indicator solution disposed on a borosilicatesubstrate. The detector may retain acceptable carbon dioxide sensitivityduring at least two hours of exposure to humid air.

An example method for determining whether a gaseous sample contains apredetermined concentration of carbon dioxide includes contacting thegaseous sample with a carbon dioxide detector having a carbon dioxidesensitive indicator disposed on a borosilicate substrate to detectcarbon dioxide in the gaseous sample.

Another embodiment relates to an endotracheal device. The device mayinclude a tubular housing having one end adapted for insertion into asubject's trachea and an other end adapted for placement external of thesubject, the housing defining a lumen therethrough from one end to theother end for allowing bidirectional passage of air into and out of thesubject to ventilate the subject's lungs. It may also include a carbondioxide detector having a carbon dioxide sensitive indicator disposed ona borosilicate substrate placed within the lumen for determining thepresence of carbon dioxide therein while still permitting unimpededbidirectional flow of air therethrough to ventilate the subject's lungs.

Yet another embodiment relates to carbon dioxide detector that includesa borosilicate substrate; and a carbon dioxide responsive indicatorsolution disposed on the borosilicate substrate, wherein the indicatorsolution changes from purple to tan in the presence of carbon dioxideabove a first level.

Yet another embodiment relates to carbon dioxide detector that includesa borosilicate substrate; and a carbon dioxide responsive indicatorsolution disposed on the borosilicate substrate, wherein the indicatorsolution changes color in less than 1 second in the presence of carbondioxide above a first level.

Finally, another embodiment relates to carbon dioxide detector thatincludes a borosilicate substrate; and a carbon dioxide responsiveindicator solution disposed on the borosilicate substrate, wherein theindicator solution is adapted to change from color in the presence ofcarbon dioxide after a shelf life of greater than five years.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure thereof may beacquired by referring to the following description taken in conjunctionwith the accompanying drawings. These drawings represent only certainembodiments of the present disclosure.

FIG. 1 illustrates a colorimetric carbon dioxide detector according toan exemplary embodiment of the present disclosure.

FIG. 2 illustrates another colorimetric carbon dioxide detector systemaccording to an exemplary embodiment of the present disclosure.

FIG. 3 illustrates a third colorimetric carbon dioxide detector systemaccording to an exemplary embodiment of the present disclosure.

FIG. 4 illustrates a resuscitator having a calorimetric carbon dioxidedetector system according to an exemplary embodiment of the presentdisclosure.

FIG. 5A shows the color transition of a previous cellulose carbondioxide detector when exposed to room air and temperature. Light hashmarks indicate yellow. Darker cross marks indicate purple.

FIG. 5B shows the color transition of a carbon dioxide detectoraccording to an embodiment of the present disclosure when exposed toroom air and temperature. Light hash marks indicate yellow. Darker crossmarks indicate purple.

FIG. 6A shows the color transition of a previous carbon dioxide detectorwhen aged at 60° C. in standard packaging. Light hash marks indicateyellow. Darker cross marks indicate purple.

FIG. 6B shows the color transition of a carbon dioxide detectoraccording to an embodiment of the present disclosure when aged at 60° C.in standard packaging. Light hash marks indicate yellow. Darker crossmarks indicate purple.

FIG. 7 shows the response time of two carbon dioxide detectors in humidair based on yellow to purple transition during inhalation and purple toyellow transition during exhalation.

While the present disclosure is susceptible to various modifications andalternative forms, specific example embodiments thereof have been shownin the drawings and are herein described in detail. It should beunderstood, however, that the description herein of specific exampleembodiments is not intended to limit the disclosure to the particularforms disclosed herein, but on the contrary, this disclosure is to coverall modifications and equivalents as defined by the appended claims.

DETAILED DESCRIPTION

The present disclosure relates to a colorimetric carbon dioxide detectorhaving a borosilicate substrate.

In a specific embodiment, shown in FIG. 1, detector 10 may includesubstrate 12 and indicator solution 14. Detector 10 may be sizedappropriately for use in a detector system, such as those shown in FIGS.2 and 3.

Substrate 12 may include any borosilicate-containing material.Specifically, it may include borosilicate fibers. These fibers may beproduced using any conventional methods, such as melt blowing andspinning. The substrate may include a mesh of borosilicate fibers. Morespecifically, it may include a thin, highly porous mesh to facilitaterapid infiltration of carbon dioxide gas into the substrate.

Borosilicate may be sufficiently hydrophilic to allow indicator solution14 to spread evenly over substrate 12 and be well absorbed when it isfirst applied. Indicator solution 14 may then be dried, but still retainsufficient water to allow reaction with carbon dioxide. However, theborosilicate substrate may also not be so hydrophobic that itsshelf-life is compromised.

The borosilicate-containing material may also include an acrylic binder.In specific embodiments, this binder may be no more than 5% by weight orvolume of the total substrate without indicator. Metrigard® membranescontaining acrylic binder sold by Pall Corporation (New York) or asimilar acrylic binder may be used.

Indicator solution 14 may contain an indicator, such as a chromogenicdye, in a solution. Indicator solution may be coated onto or impregnatedinto substrate 12. It may have a surface exposed to or near air or gaswithin carbon dioxide detector 10. Indicator solution 14 may be able torespond rapidly and positively to the presence or absence of certainconcentrations of carbon dioxide. More specifically, it may be able torespond to concentrations of carbon dioxide normally present in airrespired from a human, such as between approximately 2% and 5% orhigher. Indicator solution 14 may also be able to respond toconcentrations of carbon dioxide in air respired from a human withperfusion failure, such as concentrations between approximately 0.5% and2%. Finally, indicator solution 14 may show no response to carbondioxide concentrations normally present in external air or esophagealair, such as concentrations below approximately 0.5% and morespecifically, concentrations between 0.03% and 0.5%.

Response times to changing carbon dioxide levels in detected air may bebetween approximately 1 and 20 seconds. Further, a borosilicatesubstrate 12 may exhibit virtually instantaneous response times of lessthan 1 second, which is an improvement over typical calorimetric carbondioxide detection systems. Response may include a colorimetricindication, such as change of the indicator from one color to a verydistinct second color. However, once the color begins to change, thechange from one color to the other color may be virtually instantaneousas seen by the human eye.

In order to attain the above response properties, the indicator inindicator solution 14 may have a pK lower by 1.0-1.5 pH units than thepH of indicator solution 14. This difference allows indicator solution14 to not change color instantly when exposed to air, allowing detectorsystem 10 to be removed from packaging then connected to another device,such as a resuscitator. However, due to a greater resistance to negativeeffects of air exposure when a borosilicate or borosilicate+acrylicsubstrate is used as opposed to cellulose filter paper, an indicator pKoutside of this range may still be acceptable. In general, any pKsufficient to allow carbon dioxide detector 10 to remain exposed to roomor outside air for at least 15 minutes, at least 30 minutes, at least 60minutes, or at least 120 minutes without significant color change may besufficient.

Indicator solution 14 may include an alkaline solution containinghydroxyl ions or amine residues that react chemically with carbondioxide to form a carbonate and/or a bicarbonate or carbamate moiety.This reaction may be represented by the following equations:CO₂+H₂O⇄HCO₃ ⁻+H⁺  I.CO₂+H₂O⇄CO₃ ²⁻+2H+  II.CO₂+R₂NH⇄R₂NCOO⁻+H⁺  III.

This reaction depletes the hydroxyl ion or amine at the interfacebetween indicator solution 14 and air and this lowers the pH at thesurface of indicator solution 14 where it is adjacent or nearly adjacentto air. This depletion results in the diffusion of new base fromelsewhere in indicator solution 14 to its surface to maintain a surfacepH similar to that of indicator solution 14 overall.

More specifically, the concentration of OH⁻ or amine in the bulk ofindicator solution 14 impregnated in or coated on substrate 12 helpsdetermine the rate of diffusion of base to the surface of indicatorsolution 14. The rate of the chemical reaction at this surface isdetermined by the nature of each specific reacting species. The rate ofreaction at the surface of indicator solution 14 may be expressed by theequation R=K_(A)[CO₂][A], where [x] represents the concentration of aspecies in moles/liter and K_(A) is a constant specific for reactantspecies A. In a specific embodiment, A is the indicator.

The balance of base between the surface and remainder of indicatorsolution 14 is also influenced by the contact time between the surfaceand the gas to which it is exposed, the composition of substrate 12,which determines the diffusivity constant for A and thus the rate ofdiffusion of A to the surface, and the concentration of carbon dioxidein the gas, which determines the rate of diffusion of carbon dioxideinto or near the surface of the indicator where it may react with theindicator.

The concentration of OH⁻ or amine in indicator solution 14, the rate ofthe chemical reaction, the contact time between the indicator surfaceand the gas and the diffusivity constant for A may all be pre-determinedby the manner in which carbon dioxide detector 10 is constructed and themanner in which it is used. This leaves the concentration of carbondioxide in the gas the only variable parameter with significant effect,allowing for its measurement.

The concentration of OH⁻ or amine in indicator solution 14 and the rateof the chemical reaction may be selected such that the pH near thesurface of indicator solution 14 decreases sufficiently in the presenceof a certain concentration of carbon dioxide to cause a color change inindicator solution 14. For example, the color change may occur if theconcentration of carbon dioxide in the tested air is greater thanapproximately 2%. This color change may occur within 1 to 20 seconds ofexposure of carbon dioxide detector 10 to the air. In a specificexample, a concentration of OH⁻ sufficient to produce a pH of 9.6±0.2 inindicator solution 14 is sufficient to provide this sensitivity.

Embodiments of the present disclosure may also be utilized in areasother than breath-related carbon dioxide detectors. For example, theymay be used to monitor the air in gas storage rooms, as an indicator infood packaging, as an air freshness indicator on airplanes or otherareas where air is recycled, such as spacecraft, or as a room airfreshness indicator for any enclosed space where a high density ofpeople may gather. Sensitivity of the indicator solution and thus thedetector may be selected to meet the needs of these and otherembodiments. For example, some embodiments may need to be sensitive toand perhaps change color at different carbon dioxide concentrations thanare recommended for a breath-related detector.

As noted above, the indicator may have a pK sufficiently lower than thepH of indicator solution 14 so that a color change does not occur uponexposure to room or outside air for a certain time period. Exposure toair causes the pH at the surface of indicator solution 14 to graduallydecrease, but if such decrease is sufficiently slow, the desired timeperiod without color change limitation may still be met.

The indicator used may affect which base is used to provide an alkalineindicator solution 14. For example, if the pK of the indicator is toolow it is possible that with certain bases the pH of the indicator willnot drop low enough to cause a color change in the presence of anelevated carbon dioxide concentration. For example, when a sodiumhydroxide base is used the carbonate reaction product is water solubleand also a base. This buffers a pH decrease and may prevent the pH fromreaching a level able to trigger a color change in the indicatingelement if the indicator has a low pK.

Calcium hydroxide may be used as a base in embodiments of thisdescription. Calcium hydroxide serves as a source of hydroxyl ions butits carbonate reaction product with carbon dioxide is insoluble andtherefore unable to buffer indicator solution 14 against a decrease inpH. Thus calcium hydroxide may be used with indicators having relativelylow pKs, such as metacresol purple rather than, for example, thymol blueor phenol phthalein. This also allows for increased resistance to colorchange when exposed to room or external air. However, the use of aborosilicate or borosilicate+acrylic substrate 12 may allow use of abuffering source of hydroxyl ions in indicator solution 14.

Various colorless compounds may be used to provide an alkaline indicatorsolution 14. These include, but are not limited to calcium hydroxide,sodium carbonate, lithium hydroxide, sodium hydroxide, potassiumhydroxide, magnesium hydroxide, potassium carbonate, sodium barbitol,tribasic sodium phosphate, dibasic sodium phosphate, potassium acetate,monoethanolamine, diethanolamine, and piperidine. However, if anacrylic-bound borosilicate is used as a substrate, no base may beneeded.

Various pH sensitive indicators may also be used in indicator solution14. These include, but are not limited to metacresol purple, thymolblue, cresol red, phenol red, xylenol blue, a 3:1 mixture of cresol redand thymol blue, bromothymol blue, neutral red, phenolphthalein, rosolicacid, α-naphthelphthalein, and orange I. Other pH indicators, the colorchange that occurs, and the relevant pH as well as other information maybe found in the CRC Handbook of Chemistry and Physics, 8-17, 75thEdition 1994.

Indicator solution 14 may also contain a hygroscopic, high-boiling,transparent, colorless, water-miscible liquid. This liquid may entrapsufficient water in indicator solution 14 when it is coated onto orimpregnated into substrate 12 to allow reaction of the surface ofindicator 14 with carbon dioxide present in carbon dioxide detector 10.

Example hygroscopic, high-boiling, transparent, colorless,water-miscible liquids that may be used in indicator solution 14include, but are not limited to glycerol, propylene glycol, monoethyleneglycol, diethylene glycol, polyethylene glycol, and aliphatic alcohols.In specific embodiments, glycerol and propylene glycol or mixturesthereof may be used because of their antiseptic and non-toxicproperties. Acrylic binder used in some embodiments of the disclosurealso increases the hydrophobicity of substrate 12 and may thus decreasethe need for a hygroscopic, high-boiling, transparent, colorless,water-miscible liquid in indicator solution 14.

Indicator solution 14 may be in an aqueous solution, or it may not be insolution in water. It may require or benefit from the presence of water,or may function independently of water. Indicator solution 14 may alsobe any type of chromogenic agent. For example, it may be a chromogenicagent that does not go into solution in water, but that neverthelessrelies on nearby water.

When used, an acrylic binder provides a more basic environment for anindicator and also increases the hydrophobicity of the substrate. Abasic environment may help keep the color of the indicator appropriatein a low CO₂, such as less than 0.5%, environment. Acrylic is anelectron rich compound, which makes it a good Bronstead and Lewis base.The resulting ability to accept protons from proton rich compounds andto donate a pair of electrons to electron poor compounds allows theindicator to remain unreacted. Enough carbonic acid is formed to affectthe indicator, but some of the acid is reacted by the acrylic.

A desired ratio of proton acceptance to compound concentration may bedetermined for different detectors. Varying the concentration of theacrylic binder will have an effect on the amount of carbonic acidavailable to react with the indicator when carbon dioxide is present inlarger amounts. Thus, carbon dioxide detectors 10 that also containacrylic binder in substrate 12 may not need sodium carbonate because thebinder itself may provide a more basic environment for the indicator.When acrylic binder is used, the final color of dried indicator may alsobe less sensitive to changes in the pH of indicator solution 14. Thismay allow for a decrease in the amount of indicator in indicatorsolution 14 by as much as approximately 66% as compared tocellulose-based carbon dioxide detectors.

In a specific embodiment, used herein with all Metrigard® membranetests, indicator solution 14 may include 0.0169 g of cresol red, 275 mLtriethylene glycol, and 725 mL deionized water. This indicator solutionmay lack carbonate.

Indicator solution 14 may be immobilized on substrate 12 by drying,which removes a substantial amount of water. However, the reactionbetween the indicator and carbon dioxide may require water. Therefore,some water may be absorbed by indicator solution 14 and/or substrate 12before use. For example, water may be absorbed from ambient air. In aspecific embodiment, sufficient water may be absorbed in the time periodrequired to remove carbon dioxide detector 10 from protective packagingand begin its actual use. For example, sufficient water may be absorbedby indicator solution 14 in less than 10, 5 or 1 seconds after theopening of any protective packaging.

Indicator solution 14 may also be placed on substrate 12 in variousother forms or using other methods. For example, it may be provided in ahydrogel. Substrate 12 may also be treated, for example by plasmatreatment, prior to administration of indicator solution 14.

Use of a borosilicate substrate may result in desirable response timeand shelf life of a carbon dioxide detector, while retaining thecapacity of the detector to cycle from one color to another quickly frombreath to breath. For example, in some carbon dioxide detectors,reaction of the substrate with cresol red, which is used as a colorindicator, eventually changes the color indicator irreversibly frompurple to yellow. This change makes the detector color insensitive tothe presence or absence of carbon dioxide. As a result, the detectorsystem is no longer functional. Although packaging can help prevent thissensor aging, it nevertheless may limit shelf life. Borosilicatesubstrates do not react with cresol red. As a result, the same shelflife as is obtained with other substrates may be achieved withborosilicate and more cost effective packaging, or, a longer shelf lifeeven in the same packaging may be achieved. In certain embodiments, theshelf life of a borosilicate-based carbon dioxide detector may begreater than 5 years, great than 10 years, or greater than 14 years.Further, while the shelf life of a borosilicate-based carbon dioxidedetector may be greatly improved, the packaging employed may be reduced,due to the stability of the borosilicate-based carbon dioxide detector.While other colorimetric carbon dioxide detection systems may employdessicants to extend their shelf lives, a borosilicate-based carbondioxide detector may achieve a long shelf life (e.g. several years)without the use of a dessicant.

Additionally, the borosilicate substrate 12 may exhibit an improvedcolor cycling pattern in the presence of carbon dioxide. For example,with use of a common indicator solution 14, such as metacresol purple,the substrate 12 may change from a deep purple to a light tan color,rather than purple to yellow, in the presence of carbon dioxide. Oneadvantage of a purple-to-tan color change rather than a purple-to-yellowcolor change is that the contrast ratio between purple and tan isparticularly advantageous, allowing a healthcare worker to distinguishfiner gradations of carbon dioxide levels. Further, the purple-to-tancolor change is also helpful for people with color blindness, which mostoften impairs acuity in the green-yellow-red portion of the spectrum.

Aging of borosilicate and cellulose detector systems was evaluated underexposure to room air. A detector system having cellulose as a substratewas exposed to room temperature. Color transition from purple to yellowresults are shown in FIG. 5A. A detector system having borosilicate andacrylic as a substrate was also exposed to room temperature. Colortransition from purple to yellow results are shown in FIG. 5B.

Indicator Color (CR Scale) in all Tables and Figures where used wasdetermined using a Hunterlab LS6000 calorimeter and gas concentrationsof 0.03, 1 and 2% CO₂ (balance N₂). The CR Scale is computed from thestandard CIELab color scale as follows: CR=1.371*(a−b)+41.1. The CRcolor scale was devised so that a value of 0 corresponds to a brightyellow color while a value of 100 corresponds to deep purple. For thedata shown in FIGS. 5 and 6, the highest value of the bar is the CRvalue measured when the indicator strip was exposed to 0.03% CO₂ (e.g.“room air”). The lowest value of the bar is the CR value measured whenthe indicator strip was exposed to 2% CO₂. The total length of the baris therefore indicative of the extent of color change that is seen whenthe CO₂ concentration is transitioned between 0.03% and 2.0%. Theshading of the bar was chosen using a CR value of 40 as the visualtransition point between yellow and purple.

After only one day of exposure to air at room temperature, a significanttransition from purple to yellow had taken place when a cellulosesubstrate was used. In contrast, using a similar carbon dioxide detectorwith a borosilicate and acrylic substrate (FIG. 5B), even after 12 daysof exposure to air at room temperature, the sensitivity of the colorindicator to CO₂ was greater than after only one day of exposure for thecellulose-based detector. Results of the experiments shown in FIG. 5 arepresented in Table 1.

TABLE 1 Colorimetry of Carbon Dioxide Detectors after Aging at RoomTemperature Indicator Color (CR Scale) <0.03% CO₂ <1% CO₂ <2% CO₂Cellulose Day 0 59.2 7.6 −0.8 Day 3 −2.2 −2.4 −2.5 Day 5 −3.7 −3.3 −3.0Day 6 −1.7 −1.2 −0.8 Borosilicate + Day 0 108 57.2 43.2 acrylic Day 496.2 46.3 33.2 Day 6 84.9 37.5 26.7 Day 12 64.4 20.4 13.5

In Table 1, Metrigard® borosilicate membrane having acrylic binder (PallCorporation, New York) was used in the borosilicate and acrylicdetector.

FIG. 6A shows the rate of color change sensitivity to CO₂ in cellulosesubstrate detector systems under accelerated aging conditions. The datain FIG. 6A was collected by exposing a cellulose detector system in asealed package in the presense of desiccant to 60° C. temperatures. Theelevated temperature was used to allow the test to be performed morequickly. Elevated temperature increases the rate of cresol red reactionwith substrate 12. As FIG. 6A shows, after 3 days of the acceleratedageing experiment, the cellulose-based carbon dioxide detectors havelittle sensitivity to the presence of carbon dioxide. FIG. 6B shows asimilar test conducted with carbon dioxide detector system with aborosilicate and acrylic substrate. Even after 7 days of exposure toaccelerated aging conditions, the sensitivity of the color indicator toCO₂ was quite high. Results of the experiments shown FIG. 6 arepresented in Table 2.

TABLE 2 Colorimetry of Carbon Dioxide Detectors after Accelerated Agingat 60° C. Indicator Color (CR Scale) 0.03% 1% 2% Cellulose Day 0 77.313.4 1.5 Day 3 49.7 1.1 −6.3 Day 5 39.8 −1.4 −7.5 Day 7 33.3 −2.7 −8.0Borosilicate + Day 0 112.4 56.0 41.6 acrylic Day 3 88.6 29.4 18.9 Day 584.0 26.6 16.5 Day 7 87.8 30.8 20.3

In Table 2, Metrigard® borosilicate membrane having acrylic binder (PallCorporation, New York) was used in the borosilicate and acrylicdetector.

The performance of the borosilicate and acrylic binder-based detectordescribed above was further evaluated sealed in a pouch in the absenceof desiccant under accelerated aging conditions at even highertemperatures and for longer periods of time. Test conditions wereotherwise as indicated above. These results are provided in Table 3.

The results of Table 3, as compared to those of Table 2, indicate thatin some embodiments, a detector having a borosilicate substrate may beless sensitive to aging and have a longer shelf-life in the absence ofdesiccant rather than in its presence. Retention of acceptable carbondioxide sensitivity during accelerated aging tests correlates withshelf-life.

TABLE 3 Colorimetry of Borosilicate Carbon Dioxide Detectors afterAccelerated Aging Aged 60° C. Aged 70° C. Aged 80° C. [CO₂] 0.03% 1% 2%0.03% 1% 2% 0.03% 1% 2% Day 0 107 46.4 34.1 95.5 45.6 33.9 98.6 47.535.5 Day 1 92.7 38.1 27.7 Day 4 72.7 26.5 19.0 Day 5 71.7 26.2 18.7 Day6 93.2 39.2 28.7 70.3 27.1 19.7 Day 7 67.7 26.9 19.9 Day 9 69.1 30.023.0 Day 11 58.4 24.5 18.7 Day 13 88.4 34.5 24.7 56.7 25.4 19.8 Day 1569.6 25.5 18.3 50.6 22.8 17.8 Day 19 41.4 21.2 17.3 Day 20 84 30.8 21.9Day 22 46.8 24.0 19.5 Day 25 37.9 20.6 17.0 Day 27 82 30.7 22.2 Day 2961.1 23.4 17.3 33.6 20.1 17.0 Day 34 83.2 32.2 23.5 Day 36 59.1 23.717.8 Day 42 78.0 27.5 19.2 Day 43 50.3 20.7 15.8 Day 48 70.5 22.9 15.6Day 50 52.7 22.5 17.4 Day 55 73.1 26.3 18.7 49.7 20.7 15.8 Day 62 70.325.0 17.8

Based on these test results, a borosilicate based detector may beprovided in packaging without desiccant. This packaging may includegas-impermeable metallic foil. The device may also be sealed under anatmosphere substantially devoid of carbon dioxide. For example, thedevice may be sealed in packaging currently in use for carbon dioxidedetector systems but without the need for desiccant.

Cellulose filter paper is strongly hydrophilic so that in warm, humidair, water is rapidly absorbed into the substrate. This reduces theresponsivity of an indicator to changes in carbon dioxide concentration.The inhalation responsivity of a cellulose-based detector after exposureto humid air for certain time periods as compared to a detector of thepresent disclosure having a borosilicate and acrylic substrate is shownin FIG. 7. While both detectors show clinically useful responsiveness,The cellulose-based detector takes 13 seconds longer to respond toinhalation after 5 minutes of exposure to humid air. Data showing thisdifference is presented in FIG. 7. Response times of greater than 40seconds were not timed for their full duration.

A cellulose-based detector as compared to a detector of the currentinvention with borosilicate and acrylic substrate displays similarsensitivity to exhalation after exposure to humid air. This is incontrast to results achieved during inhalation described above. Theselevels of responsiveness are expected because the chemical reactionnecessary for color change during exhalation is less sensitive tohumidity. These results are also presented in FIG. 7. Comparative datafor both inhalation and exhalation is presented in Table 4.

TABLE 4 Response Time of Carbon Dioxide Detectors after Exposure toHumid Air Purple to Yellow Yellow to Purple (Exhalation) (sec)(Inhalation) (sec) Exposure Borosilicate + Borosilicate + Time (min)Cellulose Acrylic Cellulose Acrylic 0 1 1 9 2 5 1 1 15 2 10 2 2 26 3 153 3 34 5 20 3 4 >40 6 30 4 4 >40 8 45 5 5 >40 10 60 5 6 >40 11 120 58 >40 10

In Table 4, Metrigard® borosilicate membrane having acrylic binder (PallCorporation, New York) was used in the borosilicate and acrylicdetector.

The performance of carbon dioxide detectors in humid air is significantto clinical use because exhaled breath contains considerable amounts ofwater. Thus, performance in humid conditions is indicative ofperformance with actual patients. It may effect the use-life of adetector. Accordingly, carbon dioxide detectors having a borosilicateand acrylic substrate show faster breath-to-breath response than thosehaving a cellulose fiber substrate such as paper. This faster responseis also facilitated by the highly porous nature of borosilicate, whichallows easier penetration of air than does a cellulose fiber substrate.This may indicate a longer use-life of the borosilicate substratedetector.

In another specific embodiment, shown in FIG. 2, detector system 20 mayinclude carbon dioxide detector 10, housing 24, air intake 26, and colorindicators 28. Detector system 20 may be configured to fit into afurther system, such as resuscitator 60. The further system may supplyair to detector system 20 for measurement. Specifically, the furthersystem may be connected to the respiratory pathway of a patient.

Parts of detector system 20, such as housing 24 and/or air intake 26 maybe made from a rigid material. For example, they may be made from aplastic, such as a clear colorless, transparent plastic. By way offurther example, housing 24 and/or air intake 26 may be made frompolyethylene, polypropylene, an acrylic polymer such as PLEXIGLAS®polymer, polycarbonate, nylon, polysytrene, and styrene-acrylonitrilecopolymer. At least a portion of housing 24 may be clear so as to allowviewing of carbon dioxide detector 10.

Air intake 26 may also serve to couple detector system 20 with anyfurther system. It may be releasably secured to housing 24, such as by athreaded engagement, or it may form an integral unit with housing 24.Air intake 26 may also have a threaded engagement, tab or grooves, orother features to allow it to be releasably secured to any furthersystem. For example, a pressure fit is used to couple the detectorsystem to the manual resuscitator in the current INdGO/IndCAP™ products(Nellcor, Tyco Healthcare, California).

Color indicators 28 may approximately match the color of indicatorsolution 14 in the presence of difference levels of carbon dioxide.Color indicators 28 may also include written or other visual informationto allow a user to determine what carbon dioxide concentrations areindicated by various colors. For example, region A may show one orvarious shades that correlate with a low carbon dioxide concentration,such as below approximately 0.5% or between approximately 0.03% and0.5%. In a specific embodiment, region A may contain shades of purple.Region C may show one or various shades that correlate with a highcarbon dioxide concentration typical of respired air, such as aboveapproximately 2% or between 2% and 5%. In a specific embodiment, regionC may contain shades of yellow. Optional region B may indicate carbondioxide concentrations above that of normal or esophageal air, but belowthat corresponding with normal respiration. For example, region B mayindicate carbon dioxide concentrations common in respired air of apatient suffering from perfusion failure. Region B may show one orvarious shades that correlate with carbon dioxide concentrations ofbetween approximately 0.5% and 2%. In one specific embodiment, region Bmay contain shades of grayish purple.

In yet another specific embodiment, shown in FIG. 3, detector system 40may include carbon dioxide detector 10, housing 44, air intake 46, andcolor indicators 28. Housing 44 and air intake 46 may be similar tohousing 24 and air intake 26 in composition and function. However, theymay be of a different shape to allow use with other systems.

In another embodiment of the disclosure shown in FIG. 4 resuscitator 60may include carbon dioxide detector system 40, which attaches toresuscitator housing 56. Carbon dioxide detector system 20 may also beused with resuscitator 60 (not shown). Resuscitator 60 may also haveendotracheal tube attachment 50, swivel joint 52, and bag 54.Resuscitator 60 may be formed in any manner known to the art. Inparticular it may be formed in the manner of an INdGO™ disposable manualresuscitator (Nellcor, Tyco Healthcare, California).

Detection may include in-stream detection, such as in the currentEasyCap™ (Nellcor, Tyco Healthcare, California) system. It may alsoinclude “side-stream” detection, such as in the current INdCAP™ product(Nellcor, Tyco Healthcare, California). The detection system may bemodified to facilitate either form of detection.

Carbon dioxide detector 10 may be prepared by forming substrate 12 thenimpregnating or coating it with indicator solution 14. Substrate 12 maythen be dried to immobilize indicator solution 14 on it. Substrate 12may then be incorporated into a detector system such as those shown inFIGS. 2 and 3. The detector system may then be packaged in protectivepackaging. It may also be incorporated in a further system, such asresuscitator 60, before packaging. During its formation and handlingprior to packaging, carbon dioxide detector 10 may be kept in conditionsto minimize or control chemical reactions that might negativelyinfluence its reliability. For example, it may be kept in dry conditionsafter drying. Carbon dioxide detectors of the present disclosure mayrequire less stringent pre-packaging conditions than current cellulosefilter paper detectors because of improvements in resistance to negativeeffects of humidity and room air. Carbon dioxide detectors, detectionsystems, of further systems such as resuscitators may be created in asterile or clean environment or later sterilized.

Carbon dioxide detector 10 may be used by providing air to it. The airthen infiltrates substrate 12 and any carbon dioxide in the air reactswith indicator solution 14. This may produce a color change in theindicator. Carbon dioxide detector 10 may specifically be used to detectair from an endotracheal tube. Such systems and methods are discussed inthe U.S. patent publication No. 20080077036, titled “CARBONDIOXIDE-SENSING AIRWAY PRODUCTS AND TECHNIQUE FOR USING THE SAME” toClark R. Baker Jr., Roger Mecca, Michael P. O'Neil, and Rafael Ostrowskifiled on Sep. 25, 2006, the specification of which is herebyincorporated by reference in its entirety. The presence of carbondioxide may indicate proper placement of the tube in the trachea of apatient rather than in the esophagus. Carbon dioxide detector 10 may beable to detect such incorrect placement in sufficiently little time toallow removal of the tube and placement in the trachea before thepatient suffers serious injury or death. Change color back and forthbetween a low carbon dioxide color to a high color dioxide color mayindicate whether the patient is breathing normally. Change of color toone indicating low concentrations of carbon dioxide still aboveconcentrations in air may indicate perfusion failure in the patient.

Carbon dioxide detector 10 may be used to monitor any patient benefitingfrom an endotracheal tube or other endotracheal system, e.g. aresuscitator fitted with a mask. More specifically, if may be used tomonitor a human patient, such as a trauma victim, an anesthetizedpatient, a cardiac arrest victim, a patient suffering from airwayobstruction, or a patient suffering from respiratory failure.

While embodiments of this disclosure have been depicted, described, andare defined by reference to specific example embodiments of thedisclosure, such references do not imply a limitation on the disclosure,and no such limitation is to be inferred. The subject matter disclosedis capable of considerable modification, alteration, and equivalents inform and function, as will occur to those ordinarily skilled in thepertinent art and having the benefit of this disclosure. The depictedand described embodiments of this disclosure are examples only, and arenot exhaustive of the scope of the disclosure. For example, thesubstrate may be formed in a variety of ways; various indicators, alkalisources and other components may be used in the indicator solution; theindicator solution may be placed on the substrate in a variety of ways;multiple indicators may be used to detect narrower ranges of carbondioxide concentration; and the system may take a variety of shapes.

What is claimed is:
 1. A carbon dioxide detector comprising: aborosilicate substrate having an acrylic binder; and a carbon dioxideresponsive indicator solution disposed on the borosilicate substrate,wherein the indicator solution changes color in less than 1 second inthe presence of carbon dioxide above a first level.
 2. The carbondioxide detector according to claim 1, wherein the borosilicatesubstrate comprises a fibrous borosilicate.
 3. The carbon dioxidedetector according to claim 2, wherein the fibrous borosilicatecomprises a thin, highly porous mesh.
 4. The carbon dioxide detectoraccording to claim 1, wherein the borosilicate substrate contains lessthan approximately 5% acrylic binder by weight.
 5. The carbon dioxidedetector according to claim 1, wherein the borosilicate substratecontains less than approximately 5% acrylic binder by volume.
 6. Thecarbon dioxide detector according to claim 1, wherein the carbon dioxideresponsive indicator solution comprises an indicator.
 7. The carbondioxide detector according to claim 6, wherein the indicator comprises achromogenic dye.
 8. The carbon dioxide detector according to claim 6,wherein the indicator comprises cresol red.
 9. The carbon dioxidedetector according to claim 6, wherein the indicator comprisesmetacresol purple.
 10. The carbon dioxide detector according to claim 6,wherein the indicator comprises at least one of thymol blue, phenol red,xylenol blue, a 3:1 mixture of cresol red and thymol blue, bromothymolblue, neutral red, phenolphthalein, rosolic acid, α-naphthelphthalein,or orange I, or any combinations thereof.
 11. The carbon dioxidedetector according to claim 1, wherein the indicator solution comprisesa base.
 12. The carbon dioxide detector according to claim 11, whereinthe base comprises calcium hydroxide.
 13. The carbon dioxide detectoraccording to claim 11, wherein the base comprises at least one of sodiumcarbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide,magnesium hydroxide, potassium carbonate, sodium barbitol, tribasicsodium phosphate, dibasic sodium phosphate, potassium acetate,monoethanolamine, diethanolamine, or piperidine, or any combinationsthereof.
 14. The carbon dioxide detector according to claim 1, whereinthe indicator solution comprises a hygroscopic, high-boiling,transparent, colorless, water-miscible liquid.
 15. The carbon dioxidedetector according to claim 14, wherein the water-miscible liquidcomprises at least one of glycerol, propylene glycol, monoethyleneglycol, diethylene glycol, triethylene glycol, polyethylene glycol, oraliphatic alcohols, or any combinations thereof.
 16. The carbon dioxidedetector according to claim 1, wherein the indicator solution changesfrom purple to yellow if the presence of carbon dioxide is above apredetermined level.
 17. The carbon dioxide detector according to claim1, wherein the indicator solution changes from purple to tan if thepresence of carbon dioxide is above a predetermined level.
 18. A carbondioxide detector comprising: a borosilicate substrate having an acrylicbinder, wherein the acrylic binder is less than approximately 5% byvolume; and a carbon dioxide responsive indicator solution disposed onthe borosilicate substrate, wherein the indicator solution is adapted tochange from color in the presence of carbon dioxide after a shelf lifeof greater than five years.
 19. The carbon dioxide detector according toclaim 18, wherein the borosilicate substrate comprises a fibrousborosilicate.
 20. The carbon dioxide detector according to claim 19,wherein the fibrous borosilicate comprises a thin, highly porous mesh.21. The carbon dioxide detector according to claim 18, wherein thecarbon dioxide responsive indicator solution comprises an indicator. 22.The carbon dioxide detector according to claim 21, wherein the indicatorcomprises a chromogenic dye.
 23. The carbon dioxide detector accordingto claim 21, wherein the indicator comprises cresol red.
 24. The carbondioxide detector according to claim 21, wherein the indicator comprisesmetacresol purple.
 25. The carbon dioxide detector according to claim21, wherein the indicator comprises at least one of thymol blue, phenolred, xylenol blue, a 3:1 mixture of cresol red and thymol blue,bromothymol blue, neutral red, phenolphthalein, rosolic acid,α-naphthelphthalein, or orange I, or any combinations thereof.
 26. Thecarbon dioxide detector according to claim 18, wherein the indicatorsolution comprises a base.
 27. The carbon dioxide detector according toclaim 26, wherein the base comprises calcium hydroxide.
 28. The carbondioxide detector according to claim 26, wherein the base comprises atleast one of sodium carbonate, lithium hydroxide, sodium hydroxide,potassium hydroxide, magnesium hydroxide, potassium carbonate, sodiumbarbitol, tribasic sodium phosphate, dibasic sodium phosphate, potassiumacetate, monoethanolamine, diethanolamine, or piperidine, or anycombinations thereof.
 29. The carbon dioxide detector according to claim18, wherein the indicator solution comprises a hygroscopic,high-boiling, transparent, colorless, water-miscible liquid.
 30. Thecarbon dioxide detector according to claim 19, wherein thewater-miscible liquid comprises at least one of glycerol, propyleneglycol, monoethylene glycol, diethylene glycol, triethylene glycol,polyethylene glycol, or aliphatic alcohols, or any combinations thereof.31. The carbon dioxide detector according to claim 18, wherein theindicator solution changes color virtually instantaneously as perceivedby a human eye.
 32. The carbon dioxide detector according to claim 18,wherein the indicator solution changes from yellow to purple if thepresence of carbon dioxide is below a second level.
 33. A carbon dioxidedetector system comprising: a carbon dioxide detector comprising: aborosilicate substrate having an acrylic binder, wherein the acrylicbinder is less than approximately 5% by weight; and a carbon dioxideresponsive indicator solution disposed on the borosilicate substrate,wherein the indicator solution is adapted to change color in thepresence of carbon dioxide after a shelf life of greater than fiveyears; and a housing containing the carbon dioxide detector, the housinghaving an air intake to allow air to reach the carbon dioxide detector.34. The carbon dioxide detector system according to claim 33, whereinthe borosilicate substrate comprises a fibrous borosilicate.
 35. Thecarbon dioxide detector system according to claim 34, wherein thefibrous borosilicate comprises a thin, highly porous mesh.